Many years ago in my forties I noticed that my distant vision was beginning to degrade. I was spending a lot of time in front of the computer and I guess I was straining my eyes without realizing it. I eventually went for an eye test and was given a prescription for bifocals. At my annual medical the doc confirmed that I was only just passing the distant vision requirement. The distant correction was insignificant and so I bought some cheap reading glasses. I then always used the reading glasses when in front of the computer and of course for reading. At my next annual the doc was quite surprised when he found my distant vision had improved considerably. Obviously, straining to read had started to permanently deform my eye lenses and it wasn't until they were able to relax that my distant vision returned. Of course that was many years ago and I now need glasses for both near and distant. I use bifocals but that's just my preference.
So, before taking the eye exam, I would suggest that you not do any reading or close work for several hours prior to the test. I also have astigmatism which strangely is approximately 90 deg different in each eye, so for many years was able to get by since one eye was able to see vertical clear while the other was able to see horizontal (more or less).